It is well known to inspect semiconductor devices, for instance, those fabricated on semiconductor wafers, using a scanning electron beam inspection tool. Advantageously such electron beam inspection is not constrained by the optical (light) diffraction limits encountered by optical inspection techniques. Therefore electron beam inspection is considered useful for next generation (critical dimension less than 0.25 microns) inspection for semiconductor manufacturing. Currently commercially available electron beam-based inspection machines use a single electron beam column, based on the principle of scanning electron microscopy. The single electron beam is raster scanned over the areas of interest on a fabricated semiconductor wafer. Secondary and back-scattered electrons generated by the incident beam are detected and registered pixel-by-pixel using conventional image processing techniques to reconstruct an image of the inspected region.
Low throughput is a significant obstacle in such machines, because the images are acquired as described above pixel-by-pixel in a sequential manner. Low throughput significantly raises inspection costs and hence is undesirable.